Kay Teraoka

Peri-implant bone density in senile osteoporosis-changes from implant placement to osseointegration.

PURPOSE The aim of this study was to examine healing over time after implant body placement in a senile osteoporosis model and a control group. MATERIALS AND METHODS In this study, 16-week-old male mice were used. The senile osteoporosis model consisted of senescence-accelerated prone 6 mice and the control group consisted of senescence-accelerated resistant 1 mice. Titanium-coated plastic implants were used as experimental implants whose dimensions were 3.0 mm in length, 1.1 mm in apical diameter, and 1.2 mm in coronal diameter. Bone samples were collected at 5, 7, 14, 21, and 28 days after implant placement. A micro-quantitative computed tomography (QCT) system was used to scan these samples and a phantom in order to quantitate bone mineral measurements. Bone mineral density (BMD) of each sample was measured. Each sample was also examined by light microscopy after QCT imaging. At 14 and 28 days after implant placement, the bone-implant contact (BIC) ratios were calculated from light microscopy images and were divided into cortical bone and bone marrow regions. RESULTS When BMD was compared between the osteoporosis and control groups using micro-QCT, the osteoporosis group had a significantly lower BMD in the region 0-20 µm from the implant surface in the bone marrow region at 14 days onward after implant placement. Compared with the control group, the osteoporosis model also had significantly lower BMD in all regions 0-100 µm from the implant surface in the bone marrow region at 14 days after placement. However, in the cortical bone region, no statistically significant difference was observed in the regions at the bone-implant interface. Light microscopy revealed osseointegration for all implants 28 days after implant placement. The osteoporosis model tended to have lower BICs compared with that of the control group, although this did not reach statistical significance. DISCUSSION Our results showed that osseointegration was achieved in the osteoporosis model. However, the BMD was 30-40% lower than that of the control group in the region closest to the implant surface in bone marrow region. Peri-implant BMD was lower in a relatively large area in the osteoporosis model during an important time for osseointegration. Therefore, this result suggests that osteoporosis might be considered as a risk factor in implant therapy. CONCLUSION The osteoporosis model had a lower BMD than the control group in the region closest to the implant during an important time for osseointegration. This result suggests that senile osteoporosis might be a risk factor in implant therapy. However, the osteoporosis model and the control group had no difference in peri-implant BMD in the cortical bone region. This suggests that risk might be avoided by implant placement that effectively uses the cortical bone.

Construction of an Interconnected Pore Network Using Hydroxyapatite Beads

A new method for fabrication of macro porous grafts for bone regeneration w as presented in this study. Spherical hydroxyapatite ceramics 1 mm in diameter with a cylindrical through-hole 300 μm in diameter (HA beads) were fabricated as components of a bone g raft. By integrating the HA beads, the through-holes and inter-bead spaces were connected to each other , forming a single interconnected network. The integrated HA beads showed macro porosity of 47.7 1.9%. The interconnected macro spaces network performed remarkably concerning bone rege ration. The through-holes conducted bone formation during the 7-day-long animal test using rabbits.

Arrayed three-dimensional structures designed to induce and maintain a cell pattern by a topographical effect on cell behavior.

We investigated the ability of the microscale topography of a three-dimensional (3-D) structure arrayed on the surface of a substrate to induce and maintain a cell pattern by controlling cell behavior. Arrayed 3-D structures having different topographical characteristics, i.e., geometry and dimension, were fabricated on the surface of glass substrates by masked sand blasting. Each 3-D structure was designed to have a unit composed of a planar island for cell growth and surrounding grooves exhibiting cell repellency. The principle of the cell repellency is based on the topographical control of cell attachment, spreading, growth, and differentiation by utilizing the spatially restricted microenvironment of the grooves. Grooves with a width of less than approximately 116μm and a depth of approximately 108μm formed narrow V-shapes with a dihedral angle of less than approximately 44.4°. Cell culture experiments using osteoblast-like cells demonstrated that these narrow V-shaped grooves had sufficient cell repellency to form and maintain a cell pattern on the surface for at least 14days. From the present study, arrayed 3-D structures designed to have narrow V-shaped grooves with optimal topographical characteristics for cell repellency are promising for the formation of stable cell patterns for creating novel cell microarray platforms without using conventional protein/cell-repellent chemicals.

Preparation of Porous Poly(Lactic Acid)/Hydroxyapatite Microspheres Intended for Injectable Bone Substitutes

Porous biodegradable microspheres were successfully obtained by an improvement single step and surfactant-free emulsion solvent evaporation method. The organic phase composed of PLA and dichloromethane was stirred in aqueous phase including Ca2+ ions to yield oil in water emulsion. During emulsification, stirring rate was increased so as to produce the W/O/W emulsion that results in microspheres with internal pores. The interface of internal water/oil was stable in W/O/W emulsion, which was explained that the bond between Ca2+ ions and carboxyl group of poly(lactic acid) would be stabilized the internal water/oil interface. Adding PO4 3- aqueous solution prompted to precipitate low crystallized hydroxyapatite on the external oil/water interface, and the precipitated hydroxyapatite would stabilizied microspheres formation. The resulting microspheres were approximately 100-500 µm with internal spherical pores of 10-200 µm in diameter. The porous biodegradable microspheres were expected to be utilized as injectable bone substitutes that allow bone ingrowth and bone regeneration.

Formation of Calcium Phosphate/Titanium Oxide/Titanium/ Plastic Composite Implant

Calcium phosphate/ titanium oxide/ titanium/ plastic composite implants with 1.6-mm diameter and 7-mm length were successfully formed using a DC/ RF magnetron sputtering machine. The sample had no cracks and the surface of the sample was uniformly smooth. The chemical composition of the >10-nm-thick calcium phosphate layer was Ca: P: O=1.0: 0.79: 2.8. The sample was implanted into the tibia of an male 8-week-old SD rat for 28 days. When 0.70-μm sections of the tibia were prepared, the titanium layer with titanium oxide layer of the implant was not broken and the surfaces of the layer of the implant had not decomposed. The interaction between living bone and the implant could be clearly observed by light microscope and TEM.

Behavior of MC3T3-E1 Osteoblast-Like Cells Cultured on a Glass Substrate with Different Surface Roughness

Our experiments of mouse osteoblast-like MC3T3-E1 cells cultured on a glass substrate showed that as surface roughness of a substrate increased, cell proliferation, cell differentiation and subsequent mineralization were reduced.

An Introduction of New Artificial Bone Unit “Tetra-Bone”

We fabricated a small α-TCP ceramic unit having four pods, named “Tetra-bone” employing a ceramic injection molding. Tetra-bone can keep uniform concave geometry among the pods as well as immobilizing each other. Owing to the monotony of Tetra-bone, weight of Tetrabones used can be converted into the number of Tetra-bones, volume that can be filled with Tetrabones, and the number of functional structures. By using Tetra-bones, bone defects can be filled with intentional geometry that helps to discuss the relation between geometric features of pores and bone formation.

Effects of Through-holes' Diameter on Initial Cell Attachment and Cell Proliferation

Porous calcium phosphate ceramic biomaterials have become one of standard scaffolds to regenerate bone tissues and culture cells. The osteogenesis in scaffold is thought to be dependent on geometries of the pores in the scaffold. Ideally, pores in the scaffold are to be infiltrated by fluid elements and precursor cells. However, principle of the osteoconductive pore geometry is unclear. In this study, effects of through-holes’ diameter on initial cell attachment and proliferation were evaluated by using HA beads with various through-holes. As a result, this study confirmed a functional through-hole’s diameter that could be a principle for macropore design of the ceramic biomaterial for bone repair.

Double Layered Microshells Composed of Calcium Phosphate and Poly (lactic acid)

Biodegradable microshells were synthesized by an improvement surfactant-free emulsion solvent evaporation method. The oil in water emulsions composed of the organic phase of poly (lactic acid) in dichloromethane and the aqueous phase including Ca 2+ ions and PO4 3ions were firstly cooled down by an ice bath to stabilize emulsification. During the emulsions was returning to room temperature, calcium phosphate was rapidly precipitated at the oil/water interface, which would result in stabilizing the microshell structure on unstable liquid oil droplets. The precipitated hard calcium phosphate shells acted as a framework for poly (lactic acid) deposition by volatilization of dicloromethane. The resulting microshells were approximately 50 300 μm in diameter with the wall thickness of 1 10 μm. The walls of the microshells had a double-layered structure composed of external walls of calcium phosphate and internal walls of poly (lactic acid). The biodegradable double-layered microshells were expected to be utilized as drug delivery carriers for injectable bone substitute.

Preparation of Hydroxyapatite Ceramic Unit with a Trap for 2-D Cultured Cells

This paper demonstrated a simple technique to seed the hydroxyapatite (HA) ceramic with 2-D cultured cells to establish an advanced mode of HA grafting. The HA beads with a through-hole were fabricated to have an oblate shape to keep an opening of the through-hole contact with 2-D cultured cells layer. The seeding was performed by leaving the HA beads in a culture dish with MG63 cells in culture. The through-hole trapped MG63 cells in a sheet form by 1-day seeding. After 5 days, the number of trapped cells increased about nine fold, forming cell clumps in the through-hole. The seeding of the HA beads was considered an easy and practical method to provide HA/Cell hybrids that would realize active bone forming orthopedic treatment.